Melt together the olive oil and butter in a skillet, add leeks and saute over medium-low heat until softened and just turning golden.
Rinse the collard greens and shake off excess water, add to the leeks, and cook over medium-low heat until water is evaporated and greens start to soften, about 15 minutes. Drain and place on paper towels to remove any excess moisture.
Scatter the collard greens and leeks in an 11-inch tart pan and strew the ham artfully about. Then toss the cheese over it all.
In a medium bowl, mix together the eggs and half and half. Stir in the flour mix, adding more half and half if it seems a little thick, and pour into the tart pan.
Bake at 375 degrees for 35-40 minutes; check and bake an additional 10 minutes or until just a little jiggly and starting to become golden brown on top.